Voice calling handling method using dynamic home agency technology at the whole ip framework

ABSTRACT

The present invention provides a method for Voice Handling via Dynamic Home Agents in a Network employing All-IP Architecture, and a system for handling voice call by using this method. The method comprises the following steps: when a first RCU is about to initiate voice call with a second RCU, a first agent address FA will be assigned to a corresponding mobile RCU by the RNC in which the mobile RCU resides; when the RCUs perform the voice call, corresponding Media Gateway (MG) assigns second agent address HA 1  and HA 2  to the first and second RCUs, respectively. Wherein both HA 1  and HA 2  are only valid during this call, and when the call is terminated or dropped, HA 1  and HA 2  will be released back to the pool of the IP addresses of the corresponding MG. The first and second RCUs implement the voice call based on the assigned first and second agent addresses. This method handles voice calls services via Dynamic Home Agents technique in MobileIP, so as to reduce the number of propagation of the IP header in communication channel in a wireless environment, and enhance system resources utilization efficiency.

TECHNICAL FIELD

The present invention relates generally to a method for handling voicecall in an all-IP network, and in particular, to a method for voice callhandling via dynamic home agents in the wireless communication networkemploying the all-IP architecture, and to a wireless communicationsystem for handling voice call utilizing this method.

BACKGROUND OF THE RELATED ART

In the current 3GPP release 4 architecture, both core-network (CN) andthe interfaces connecting radio network controllers (RNC) and CN areIP-based, and during handling of the voice calls traffic, for example,fixed IP technique has been employed, that is, an exclusive IP-addressis assigned respectively to each wireless communication unit (RCU)requesting a voice call such as a PSTN network phone and a mobilesubscriber UE (User Equipment), subsequently leading to deterioration ofsystem resources utilization efficiency. As is known, IP addressresources are quite scare in the wireless communication system employingthe all-IP architecture, therefore a new technique differing fromconventional fixed-IP of assigning to each RCU that requestes a voicecall is necessary.

In addition thereto, the system architecture in the prior art isdisadvantaged by adopting different protocols for different servicessuch as CS and PS, for example, the Megaco-protocol-based CS servicetransmission method and GTP-protocol-based PS transmission method incurrent 3GPP Release 4 architecture. This will make the systemarchitectures and the type of the service not uniform, thus leading toreduction in utilization efficiency of communication resources andservice efficiency.

SUMMARY OF THE DISCLOSURE

It is therefore an object of the present invention to overcome thedisadvantages in the prior art, and the following technical solutionshave been adopted to achieve the object.

According to a first aspect of the present disclosure, a method ofhandling voice call between Radio Communication Units (RCUs) of awireless communication system in an all-IP architecture is provided. Thewireless communication system comprises Core Network (CN) consisting ofMobile switch center MSC and Gateway Mobile Switch Center (GMSC), RadioNetwork Subsystem (RNS) consisting of a plurality of Radio NetworkControllers (RNCs), and a plurality of RCUs. Said method comprising thefollowing steps: A) when a first RCU is about to initiate voice callwith a second RCU, a first agent address FA will be assigned to acorresponding mobile RCU via the RNC in which the mobile RCU resides; B)when the first RCU requests to talk to the second RCU, correspondingMedia Gateway (MG) assigns a second agent address HA1 to the first RCUand assigns a second agent address HA2 to the second RCU, wherein bothHA1 and HA2 are only valid during this call and are applied in mobile IProuting addressing of the all-IP network, and when the call isterminated or dropped, HA1 and HA2 will be released back to the pool ofthe IP addresses of the corresponding MG; C) carrying out appropriateresource configuration for corresponding RNC in which said first andsecond RCUs reside or the corresponding MG; D) transmitting VoIP datapackets between said RNC of the two RCUs or corresponding MG accordingto said first agent address FA and said second agent addresses HA1 andHA2, thereby implementing voice call between said two RCUs.

According to an embodiment of the present invention, IP encapsulationwill be effected for the transmitted VoIP data packets by means of saidfirst agent address FA, said second agent addresses HA1 and HA2 in StepD, so that tunnels for transmitting said data packets will beestablished in foreign agents, avoiding need of transmitting an outer IPheader in the radio section.

According to another embodiment of the present invention, the secondagent address HA1 is assigned to the first RCU and the second agentaddress HA2 is assigned to the second RCU in accordance with the IPaddresses distribution status in the pool of the IP addresses ofcorresponding MG. The assigned IP addresses can be re-assigned to otherRCUs only after being released, and the IP addresses for MG at differentlocations differ from each other.

According to another embodiment of the present invention, said first RCUis a Mobile Station (MS), said second RCU is a PSTN phone, and the RNCin which the MS resides assigns an foreign agent address FA1 to the MSas its first agent address. When the two RCUs start a voice call, thePSTN MG assigns a temporary home agent address HA1 to the MS as itssecond agent address, and at the same time assigns a temporary IPaddress HA2 to the PSTN phone as its second agent address. IPencapsulation is performed on the data packets carrying voices from thePSTN MG to the RNC in which the MS resides by means of inner and outerIP headers, and wherein the source and destination addresses of theouter IP header of the data packet are HA2 and FA1, respectively, andthe source and destination addresses of the inner IP header of the datapacket are HA2 and HA1, respectively.

According to yet another embodiment of the present invention, said firstRCU is a first MS, the second RCU is a second MS, and RNC1 in which thefirst MS resides assigns a foreign agent care-of address FA1 to the MSas its first agent address, RNC2 in which the second MS resides assignsa foreign agent care-of address FA2 to the MS as its first agentaddress. When the two RCUs start a voice call, corresponding MG assignsa temporary home agent address HA1 to the first MS as its second agentaddress, and at the same time assigns a temporary home agent address HA2to the second MS as its second agent address. IP encapsulation isperformed on the uplink data packets from the first MS to the second MSby means of inner and outer IP headers, wherein the source anddestination addresses of outer IP header of the data packets are HA1 andFA2, respectively, and the source and destination addresses of inner IPheader of the data packet are HA1 and HA2, respectively. IPencapsulation is performed on the uplink data packets from the second MSto the first MS, wherein the source and destination addresses of outerIP header of the packet are HA2 and FA1, respectively, and the sourceand destination addresses of inner IP header of the data packets are HA2and HA1, respectively.

According to yet another embodiment of the present invention, when themobile RCU in said RCUs registers with another RNC′ which is differentfrom the RNC in which said mobile RCU currently resides during theprocess of the voice call, said method further comprises the followingsteps: the another RNC′ assigning a new foreign agent care-of addressFA′ to said mobile RCU as its first agent address while its second agentaddress remains unchanged; the VoIP data packets being transmittedbetween the two RCUs in accordance with the new foreign agent care-ofaddress FA′.

According to a second aspect of the present invention, a wirelesscommunication system employing an all-IP architecture is provided. Thewireless communication system comprises Core Network (CN) consisting ofMobile switch center MSC and Gateway Mobile Switch Center (GMSC), RadioNetwork Subsystem (RNS) consisting of a plurality of Radio NetworkControllers (RNCs), and a plurality of RCUs, characterized in that saidsystem further comprising: means for assigning a first agent address FAto a corresponding mobile RCU when a first RCU is about to initiatevoice call with a second RCU; means for assigning a second agent addressHA1 to the first RCU and assigning a second agent address HA2 to thesecond RCU when the first RCU requests to talk to the second RCU,wherein both HA1 and HA2 are only valid during this call, and when thecall is terminated or dropped, said HA1 and HA2 are released back to thepool of the IP addresses of corresponding MG; means for carrying outappropriate resource set-up for corresponding MG and the RNC in whichthe first and second RCUs reside; and means for transmitting VoIP datapackets between the RNC of said two RCUs or corresponding MG accordingto said first agent address FA, said second agent addresses HA1 and HA2,thereby implementing voice call between said two RCUs.

According to an embodiment of the wireless communication systemaccording to the present inveiton, the system further comprises meansfor performing IP encapsulation for the transmitted VoIP data packetsaccording to said first agent address FA and said second agent addressesHA1 and HA2, so that tunnels for transmitting said data packets can beestablished in foreign agents, avoiding need of transmitting an outer IPheader in the radio section.

According to another embodiment of the wireless communication system ofthe present inveiton, the system further comprises means for assigningthe second agent address HA1 to the first RCU and assigning the secondagent address HA2 to the second RCU in accordance with IP addressdistribution status in the pool of the IP addresses of corresponding MG,wherein the assigned IP addresses can be re-assigned to other RCUs onlyafter being released, and the IP addresses in the MG at differentlocations are different form each other.

According to yet another embodiment of the wireless communication systemof the present inveiton, said first RCU is a MS and said second RCU is aPSTN phone, and the RNC in which the MS resides assigns a foreign agentaddress FA1 to the MS as its first agent address. When the two RCUsstart a voice call, the PSTN MG assigns to the MS a temporary home agentaddress HA1 as its second agent address, and at the same time assigns atemporary IP address HA2 to the PSTN phone as its second agent address.IP encapsulation is performed on the data packets carrying voices fromPSTN MG to RNC in which the MS resides by means of inner and outer IPheaders, wherein the source and destination addresses of the outer IPheader of the data packet are HA2 and FA1, respectively, and the sourceand destination addresses of the inner IP header of the data packets areHA2 and HA1, respectively.

According to yet another embodiment of the wireless communication systemof the present inveiton, said first RCU is a first MS, and said secondRCU is a second MS. RNC1 in which the first MS resides assigns a foreignagent care-of address FA1 to the MS as its first agent address, and RNC2in which the second MS resides assigns a foreign agent care-of addressFA2 to the MS as its first agent address. When the two RCUs start avoice call, corresponding MG assigns a temporary home agent address HA1to the first MS as its second agent address, and at the same timeassigns a temporary home agent address HA2 to the second MS as itssecond agent address. IP encapsulation is performed on the uplinkpackets from the first MS to the second MS by means of inner and outerIP headers, wherein the source and destination addresses of the outer IPheader of the data packets are HA1 and FA2, respectively, and the sourceand destination addresses of the inner IP header of the data packets areHA1 and HA2, respectively. IP encapsulation is performed on the uplinkpackets from the second MS to the first MS, wherein the source anddestination addresses of the outer IP header of the packet are HA2 andFA1, respectively, and the source and destination addresses of the innerIP header of the packet ale HA2 and HA1, respectively.

According to yet another embodiment of the wireless communication systemof the present inveiton, when the mobile RCU in said RCUs registers withanother RNC′ which is different from the RNC in which said mobile RCUcurrently resides during the process of the voice call, the another RNC′assigns a new foreign agent care-of address FA′ to said mobile RCU asits first agent address while its second agent address remainsunchanged, and the VoIP data packets are transmitted between the twoRCUs according to the new foreign agent care-of address FA′.

As can be concluded from above discourses, voice call handling asincluded in the present invention has been optimized and thus differsfrom the conventional voice call setup and handling procedures. Morespecifically, the present invention proposes a novel method to controlthe mobility and call handling of voice services in the all-IParchitecture. The method utilizes dynamic home agent technique inMobileIP to handle voice calls services. This method helps to reduce thenumber of propagation of the IP header in communication channel in awireless environment, and enhance system resources utilizationefficiency due to the dynamic assignment and release of care of IPaddresses.

Further, the present invention applies MobileIP technique totransmission technique for the call service (CS) in 3G all-IP network.As compared with existing Megaco-protocol-based CS transmission methodand GTP-protocol-based PS transmission method in current 3GPP release 4architecture, the MobileIP-based CS and PS services may share a commonsystem architecture, which makes the system architecture independentfrom the type of services. Moreover, if identical MobileIP architectureis utilized, at least one skip node can be reduced for PS serviceuplink, thus increasing service efficiency of the wireless communicationsystem.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the presentinvention will become more apparent from the following detaileddescription when taken in conjunction with the accompanying drawings inwhich:

FIG. 1 is a flow chart illustrating an embodiment utilizing the methodfor voice call handling according to the present invention;

FIG. 2 is a diagram illustrating IP encapsulation of the data packetscarrying voices in accordance with the embodiment in FIG. 1;

FIG. 3 is a flow chart illustrating another embodiment of the method forvoice call handling according to the present invention;

FIG. 4 is a diagram illustrating the structure of a wirelesscommunication system based on 3GPP Release 4;

FIG. 5 is a diagram illustrating the structure of a wirelesscommunication system based on the dynamic IP technique of the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1, this figure is a flow chart illustrating anembodiment utilizing the method for voice call handling according to thepresent invention. As shown in this Figure, the wireless communicationnetwork based on the all-IP architecture comprises the CN consisting ofPSTN MG, MSC (Mobile switch center) server and GMSC (Gateway MobileSwitch Center) server, PSTN, RNC and a plurality of Mobile terminalsubscriber UE. This Figure illustrates the procedure of the voice callbetween a UE and a PSTN phone only in an illustrative but not in arestrictive way.

When the UE roams to an area served by a certain RNC, the RNC willassign a MobileIP foreign agent care-of address to the UE. The assignedaddress is the address of serving dedicated resource board in the RNC,the dedicated resource board may support a plurality of subscribers andmanaged/controlled by the RNC. This address is also called UE-FA-Address(FA). The RNC will subsequently update the care-of address of the UE inthe Location Server (Step S200). As for incoming calls from PSTN to UE,GMSC server firstly receives the call request from the PSTN (Step S100);the GMSC server retrieves the current location (RNC address) of the UEfrom the Location Server (Step S110); then, the GMSC server asks thecorresponding PSTM MG to assign a dynamic home agent IP address(UE-Call-Address) within its subnet to the UE for that particular call(Step S120). A UE is assigned a temporary home agent (HA) address,UE-Call-Address, when it requests for voice call services. This HA IPaddress is only valid during the call and will be used for MobileIProuting in the all-IP network. When the call is terminated or dropped,the HA IP address will be released and return to the pool of IPaddresses owned by the PSTN MG. This mode conserves to the best extentaddress space of the care-of address of the FA, and the care-of addressof the FA can be shared by all connected UEs rather than exclusivelyused by each UF. When a PSTN phone asks for voice call with a certainUE, the GMSC server asks corresponding PSTN MG to assign a correspondingnode IP address (PSTN-Phone-Address) within its subnet to the sourcePSTN phone for that particular call (Step S120). This IP address(PSTN-Phone-Address) is only temporary, and valid only during the calland will be used for MobileIP routing in the all-IP network. When thecall is terminated or dropped, the IP address will be released andreturn to the pool of IP addresses owned by the PSTN MG. The GMSC serverwill then set up appropriate resources in the PSTN MG (Step S130); theGMSC server talks to the MSC server in which the UE Mobility Management(MM) context resides (Step S140); the MSC server sets up appropriateresource in the RNC that the UE roams to (Step S150); the MSC servertransfers the incoming PSTN call processing to Call Control/MobilityManagement (CC/MM) unit in 3G and sends it to the UE (Step S160). TheRNC and PSTN MG start to send/receive VoIP data packets via MobileIP(Step S170).

The basis for assigning temporary IP address to a UE and a PSTN phone asdescribed abode is that the assigned IP addresses can be re-assigned toother PSTN or UE only when they are released. IP addresses in PSTN MG atdifferent locations differ from each other, for example, in Beijing itcould be 200.xxx.xxx.xxx while in Shenzhen it could be 201.xxx.xxx.xxx.According to the number of the accessed local MG subscribers, certainnumber of IP addresses remain un-assigned in the pool of the IPaddresses. For the incoming call from PSTN to UE, the PSTN and UE willbe assigned randomly a temporary PSTN-Phone-Address and a temporaryUE-Call-Address, respectively. When the call is terminated or dropped,the two IP addresses will be released and can be re-assigned by PSTN MGto other call services.

Descriptions of the process for IP encapsulation of data packetssent/received between the PSTN phone and UE requesting a voice call lowill be given in conjunction with FIG. 2. For the downlink IP datapackets from the PSTN MG to RNC, IP encapsulation is required. That is,an inner IP packet carrying voice is encapsulated with an outer IPaddress. The source IP address of the outer IP header isPSTN-Phone-address, and the destination IP address of the outer IPheader is UE-FA-Address (FA). The source IP address of the inner IPheader is PSTN-Phone-address, and the destination IP address of theinner IP header is the UE-Call-Address (HA). In a wireless environmentwhere radio resources are scarce, the adoption of foreign agents meansthat the channel is established in the foreign agents and there is noneed of transmitting the outer IP header in the radio section, thusenhancing radio resource utilization efficiency. For the uplink datapackets from the RNC to the PSTN MG, IP encapsulation will not beneeded. The source IP address of the IP header is UE-Call-Address (HA)and the destination IP address is PSTN-Phone-address.

By means of this encapsulation method, the encapsulated packets aredelivered to a foreign agent which strips the foreign IP address andforwards the inner IP packets to UE via radio channels. As forconventional techniques, the home agent forwards the whole encapsulateddata packets directly to UE who will open the outer IP address andprocess inner IP data packets. In a wireless environment where radioresources are scarce, the adoption of foreign agents means that thechannel is established in the foreign agents and there is no need oftransmitting the outer IP header in the radio section, thus enhancingradio resource utilization efficiency.

The above said dynamic home agent technique and IP encapsulation methodmay also be applied to the handling of voice call between UEs. Themechanism for the handling of voice call between UEs is similar as themechanism for UE-PSTN voice service, except that this mechanism combinesthe two mechanisms of UE-PSTN and PSTN-UE. FIG. 3 is a flow chartillustrating another embodiment of the method for voice call handlingaccording to the present invention, wherein the voice call is occurredbetween UE-A and UE-B. As in UE-PSTN voice call handling process, theRNC-A and RNC-B in which UE-A and UE-B resides, respectively, assignforeign agent care-of addresses UE-FA-Address (FA1) and UE-FA-Address(FA2) to RNC-A and RNC-B.

When UE-A requests to talks to UE-B, UE-UE CS MG will assign temporarydynamic home agent addresses UE-CALL-Address (HA1) and UE-CALL-Address(HA2) to UE-A and UE-B, respectively. It shall be noted herein that inthis situation, there is no need to assign a corresponding IP addressesto the voice call, because all entities have their own IP addresses. Asto UE-A, its foreign agent care-of address is UE-FA-Address (FA1), itsdynamic home agent address is UE-Call-Address (HA1), and the IP addressof the corresponding voice calling entity is UE-Call-Address (HA2); Asto UE-B, its foreign agent care-of address is UE-FA-Address (FA2), itsdynamic home agent address UE-Call-Address (HA2), and the IP address ofthe corresponding voice calling entity is UE-Call-Address (HA1).

Therefore, when UE-A requests to talk to UE-B, as to the uplink fromUE-A to UE-B as shown by the triangle route illustrated by arrows inFIG. 3, the UE-A sends VoIP data packets directly to its correspondingIP node, that is, from UE-CALL-address (HA1) to UE-Call-Address (HA2).However, when UE-UE CS MG receives the IP packets, it forwards thepackets by tunneling technique to the foreign agent care-of addressUE-FA-Address (FA2) of UE-B. That is to say, the IP data packets sent bytunneling technique shall be subjected to IP encapsulation,with thesource address and the destination address for the outer IP header beingUE-Call-Address (HA1) and UE-FA-Address (FA2), respectively, and thesource address and the destination address for the inner IP header beingUE-Call-Address (HA1) and UE-HA-Address (HA2), respectively.

Similarly, when UE-B requests to talk to UE-A, the mechanism asmentioned above also can be used to process the voice call.

Likewise, the above said method according to the present invention canalso be applied to handle corresponding voice call service when the UEbeing in the voice call initiates handoff, and process of the handlingwill be described based on FIG. 1. As illustrated in FIG. 1, when the UEroams from one RNC to another RNC during a call, the new RNC assigns anew care-of address to the UE; the new RNC will then update the LocationServer; the Location Serversubsequently updates the care-of address ofthe UE in the GMSC server; the GMSC talks to PSTN MG; the PSTN MGupdates the new care-of address of the UE; the new RNC and PSTN MG startto send/receive VoIP data packets via MobileIP according to the abovesaid voice call handling method. It therefore can be concluded that bymeans of employing the dynamic home agent address technology, when theUE initiates handoff the call will not be interrupted, and so that softhandoff can be realized.

Likewise, two UEs which are performing a voice call can also achievesoft handoff using the same handling method described above.

FIGS. 4 and 5 respectively illustrate the structural diagrams of awireless communication system based on 3GPP Release 4 and on the dynamicIP technique according to the present invention. In the field of Release4 PS, SGSN is responsible for transmission of both data and signalstream. But in CS field, transmission of signal and data streams isseparate. Media Gateway (MGW) is responsible for transmission of bothsignal and data while MSC is only responsible for transmission of signalstream. MSC is responsible for voice call handling in CS field, and CallControl/Mobility Management (CC/MM). The solidlines in FIGS. 4 and 5indicate the common transmission path for signal and data while dottedlines indicates only signal transmission. In the MobileIP-based newarchitecture, SGSN is responsible only for the transmission of signals,as indicated by the dotted lines in FIG. 5. SGSN still handles GMM/SMfor PS field, while MGW only handles PS data transmission. By means ofseparating the transmission of signals and data stream, PS and CS sharethe same system architecture. In Release 4, GTP-based Gn interface isused for both signal and data transmission, while in the all-IP newarchitecture, Gn-new is used only for signal transmission.

In PS field of Release 4, mobility control and data transmissionmechanism are both GTP-based, while in the new architecture, PS fieldmobility control and data transmission mechanism are MobileIP-based. ForPS service uplink, at least one skip node can be eliminated, i.e. theSGSN in the old architecture can be omitted, as shown in FIG. 5.

In CS field of Release 4, mobility control and data transmissionmechanism are both Megaco-based, while in the new architecture CS fieldmobility control and data transmission mechanism are MobileIP-based. TheRNC in UTRAN is the foreign agent, and the MGW connected with PSTN isthe home agent.

The present invention applies MobileIP technique to call service (CS)transmission in 3G all-IP network. As compared with current Megaco-basedCS transmission method and GTP-based PS transmission method in 3GPPRelease 4 (as shown in FIG. 4), MobileIP-based CS and PS services mayshare the same system architecture, which makes the system architectureindependent from the type of services. Moreover, if identical MobileIParchitecture is utilized, at least one skip node can be reduced for PSservice uplink, i.e., the SGSN in the old architecture can be omitted.As shown in FIG. 5, GGSN is the Home Agent, and MGW is the ForeignAgent.

Numerous characteristics and advantages of representative embodiments ofthe present invention have been set forth in the foregoing description.It is to be understood, however, that while particular forms orembodiments of the invention have been illustrated, variousmodifications can be made without departing from the sprit and scope ofthe invention.

1. A method of handling voice call between Radio Communication Units(RCUs) of a wireless communication system in an all-IP architecture,wherein said wireless communication system comprises Core Network (CN)consisting of Mobile switch center MSC and Gateway Mobile Switch Center(GMSC), Radio Network Subsystem (RNS) consisting of a plurality of RadioNetwork Controllers (RNCs), and a plurality of RCUs, said methodcomprising the following steps: A) when a first RCU is about to initiatevoice call with a second RCU, a first agent address FA will be assignedto a corresponding mobile RCU via the RNC in which the mobile RCUresides; B) when the first RCU requests to talk to the second RCU,corresponding Media Gateway (MG) assigns a second agent address HA1 tothe first RCU and assigns a second agent address HA2 to the second RCU,wherein both HA1 and HA2 are only valid during this call and are appliedin mobile IP routing addressing of the all-IP network, and when the callis terminated or dropped, HA1 and HA2 will be released back to the poolof the IP addresses of the corresponding MG; C) carrying out appropriateresource configuration for corresponding RNC in which said first andsecond RCUs reside or the corresponding MG; D) transmitting VoIP datapackets between said RNC of the two RCUs or corresponding MG accordingto said first agent address FA and said second agent addresses HA1 andHA2, thereby implementing voice call between said two RCUs.
 2. Themethod according to claim 1, wherein IP encapsulation will be effectedfor the transmitted VoIP data packets by means of said first agentaddress FA, said second agent addresses HA1 and HA2 in Step D, so thattunnels for transmitting said data packets will be established inforeign agents, avoiding need of transmitting an outer IP header in theradio section.
 3. The method according to claim 1, wherein the secondagent address HA1 is assigned to the first RCU and the second agentaddress HA2 is assigned to the second RCU in accordance with the IPaddresses distribution status in the pool of the IP addresses ofcorresponding MG, and the assigned IP addresses can be re-assigned toother RCUs only after being released, and the IP addresses for MG atdifferent locations differ from each other.
 4. The method according toclaim 1, wherein said first RCU is a Mobile Station (MS), said secondRCU is a PSTN phone, and the RNC in which the MS resides assigns anforeign agent address FA1 to the MS as its first agent address; when thetwo RCUs start a voice call, the PSTN MG assigns a temporary home agentaddress HA1 to the MS as its second agent address, and at the same timeassigns a temporary IP address HA2 to the PSTN phone as its second agentaddress; IP encapsulation is performed on the data packets carryingvoices from the PSTN MG to the RNC in which the MS resides by means ofinner and outer IP headers, and wherein the source and destinationaddresses of the outer IP header of the data packet are HA2 and FA1,respectively, and the source and destination addresses of the inner IPheader of the data packet are HA2 and HA1, respectively.
 5. The methodaccording to claim 1, wherein said first RCU is a first MS, the secondRCU is a second MS, and RNC1 in which the first MS resides assigns aforeign agent care-of address FA1 to the MS as its first agent address,RNC2 in which the second MS resides assigns a foreign agent care-ofaddress FA2 to the MS as its first agent address; when the two RCUsstart a voice call, corresponding MG assigns a temporary home agentaddress HA1 to the first MS as its second agent address, and at the sametime assigns a temporary home agent address HA2 to the second MS as itssecond agent address; IP encapsulation is performed on the uplink datapackets from the first MS to the second MS by means of inner and outerIP headers, wherein the source and destination addresses of outer IPheader of the data packets are HA1 and FA2, respectively, and the sourceand destination addresses of inner IP header of the data packet are HA1and HA2, respectively; and IP encapsulation is performed on the uplinkdata packets from the second MS to the first MS, wherein the source anddestination addresses of outer IP header of the packet are HA2 and FA1,respectively, and the source and destination addresses of inner IPheader of the data packets are HA2 and HA1, respectively.
 6. The methodaccording to claim 1, wherein when the mobile RCU in said RCUs registerswith another RNC′ which is different from the RNC in which said mobileRCU currently resides during the process of the voice call, said methodfurther comprises the following steps: E) the another RNC′ assigning anew foreign agent care-of address FA′ to said mobile RCU as its firstagent address while its second agent address remains unchanged; F) theVoIP data packets being transmitted between the two RCUs in accordancewith the new foreign agent care-of address FA′.
 7. A wirelesscommunication system employing an all-IP architecture, comprising CoreNetwork (CN) consisting of Mobile switch center MSC and Gateway MobileSwitch Center (GMSC), Radio Network Subsystem (RNS) consisting of aplurality of Radio Network Controllers (RNCs), and a plurality of RCUs,characterized in that said system further comprising: means forassigning a first agent address FA to a corresponding mobile RCU when afirst RCU is about to initiate voice call with a second RCU; means forassigning a second agent address HA1 to the first RCU and assigning asecond agent address HA2 to the second RCU when the first RCU requeststo talk to the second RCU, wherein both HA1 and HA2 are only validduring this call, and when the call is terminated or dropped, said HA1and HA2 are released back to the pool of the IP addresses ofcorresponding MG; means for carrying out appropriate resource set-up forcorresponding MG and the RNC in which the first and second RCUs reside;means for transmitting VoIP data packets between the RNC of said twoRCUs or corresponding MG according to said first agent address FA, saidsecond agent addresses HA1 and HA2, thereby implementing voice callbetween said two RCUs .
 8. The wireless communication system accordingto claim 7, further comprising means for performing IP encapsulation forthe transmitted VoIP data packets according to said first agent addressFA and said second agent addresses HA1 and HA2, so that tunnels fortransmitting said data packets can be established in foreign agents,avoiding need of transmitting an outer IP header in the radio section.9. A wireless communication system according to claim 7, furthercomprising means for assigning the second agent address HA1 to the firstRCU and assigning the second agent address HA2 to the second RCU inaccordance with IP address distribution status in the pool of the IPaddresses of corresponding MG, wherein the assigned IP addresses can bere-assigned to other RCUs only after being released, and the IPaddresses in the MG at different locations are different form eachother.
 10. The wireless communication system according to claim 8,wherein said first RCU is a MS and said second RCU is a PSTN phone, andthe RNC in which the MS resides assigns a foreign agent address FA1 tothe MS as its first agent address; when the two RCUs start a voice call,the PSTN MG assigns to the MS a temporary home agent address HA1 as itssecond agent address, and at the same time assigns a temporary IPaddress HA2 to the PSTN phone as its second agent address; IPencapsulation is performed on the data packets carrying voices from PSTNMG to RNC in which the MS resides by means of inner and outer IPheaders, wherein the source and destination addresses of the outer IPheader of the data packet are HA2 and FA1, respectively, and the sourceand destination addresses of the inner IP header of the data packets areHA2 and HA1, respectively.
 11. The wireless communication systemaccording to claim 8, wherein said first RCU is a first MS, and saidsecond RCU is a second MS; RNC1 in which the first MS resides assigns aforeign agent care-of address FA1 to the MS as its first agent address,and RNC2 in which the second MS resides assigns a foreign agent care-ofaddress FA2 to the MS as its first agent address; when the two RCUsstart a voice call, corresponding MG assigns a temporary home agentaddress HA1 to the first MS as its second agent address, and at the sametime assigns a temporary home agent address HA2 to the second MS as itssecond agent address; IP encapsulation is performed on the uplinkpackets from the first MS to the second MS by means of inner and outerIP headers, wherein the source and destination addresses of the outer IPheader of the data packets are HA1 and FA2, respectively, and the sourceand destination addresses of the inner IP header of the data packets areHA1 and HA2, respectively; and, IP encapsulation is performed on theuplink packets from the second MS to the first MS, wherein the sourceand destination addresses of the outer IP header of the packet are HA2and FA1, respectively, and the source and destination addresses of theinner IP header of the packet are HA2 and HA1, respectively.
 12. Thewireless communication system according to claim 7, wherein when themobile RCU in said RCUs registers with another RNC′ which is differentfrom the RNC in which said mobile RCU currently resides during theprocess of the voice call, the another RNC′ assigns a new foreign agentcare-of address FA′ to said mobile RCU as its first agent address whileits second agent address remains unchanged, and the VoIP data packetsare transmitted between the two RCUs according to the new foreign agentcare-of address FA′.